1. Field of the Invention
The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with an automated system and method for ultrasonically cleaning fuel rod tubes which is used near the end of the tube fabrication process.
2. Description of the Prior Art
In most nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend above and below the opposite ends of the fuel rods.
The fuel rods each contain fissile material and are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. All materials present into the reactor core will be irradiated by the fissile material in the fuel rods and, in turn, will interact with it. In order to produce the desired neutron flux in the core, the nuclear interaction and thus the chemical composition of all components introduced into the reactor core must be known and taken into consideration. Therefore, the materials composing all such components are carefully selected in order to obtain the desired interaction with the neutron flux.
To control what materials are introduced into the core, extensive measures and steps are taken to maintain a clean environment not only in the reactor facility itself but also in the facilities where the components are manufactured. One part of this overall effort toward achieving a high standard of cleanliness is the cleaning of component parts during fabrication to remove foreign matter therefrom. In the case of the tubes used in fuel rods, one of the final steps in their fabrication is a thorough cleaning of the interior and exterior of each tube. The conventional cleaning technique used involves bundling large numbers of tubes, for example three hundred, in a group, submerging the bundle into a tank of cleaning solution for a predetermined time, and then submerging the bundle into a rinse tank to flush impurities from the tube surfaces.
However, there are several problems with this conventional technique. First, the tube cleaning solution typically used is methylene chloride toluene which is environmentally undesirable. Also, the steps of gathering and bundling the tubes are inherently inefficient and cumbersome, while the manipulation of the large bundles of tubes demands the use of a crane and operator. Consequently, a need has emerged to improve and automate the way in which fuel rod tube cleaning is carried out.